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5 Things You Need to Know About Natural Gas Vehicles (NGVs)
By Jennifer Olvera
The Basics About Natural Gas Vehicles
Natural gas, a blend of hydrocarbons comprised mostly of methane, is touted as one of the cleanest, safest, and most beneficial forms of energy. This is because it has the highest hydrogen-to-carbon ratio of any hydrocarbon fuel and it produces fewer greenhouse gases and particulate matter that its counterparts. Natural gas vehicles operate similarly to gasoline-powered vehicles: fuel mixes with air, is fed into the cylinders, and is ignited by a spark plug that moves the piston up and down to create power.
Storage of Natural Gas
The majority of natural gas vehicles use compressed natural gas (CNG). It's stored in vehicles at high pressure – 3,000-3,600 pounds per square inch – in tube-shaped cylinders. Natural gas also can be stored in its liquefied form as LNG, but first it must be cooled to -260 degrees Fahrenheit and kept in thermal storage tanks on board vehicles. Liquid natural gas (LNG) vehicles' main benefit is LNG requires substantially less storage space than CNG.
Fueling Natural Gas Vehicles
Unlike gasoline and diesel fueled vehicles, which use liquid at a ambient temperature and pressure and can in theory have "open" systems, CNG and LNG storage systems must be closed so no fuel can escape. Natural gas is fueled by pressure-fit nozzles that lock into the fuel receptacle so that, once the nozzle is removed, no gas escapes.
How Natural Gas Stations Work
Usually, gas at CNG stations is taken from the local gas utility line at a low-pressure. It then gets compressed and is stored in storage tanks at high pressure. There are two types of equipment for fueling natural gas: fast-fill, which uses a large compressor and a high-pressure storage tank system; and time-fill, which has a smaller and less costly compressor and no storage and takes about an hour per gallon to fill. Time-fill can be done with a special fueling appliance at home.
How a Natural Gas Engine Works
Natural gas flows from the storage cylinders to the fuel line when a natural gas vehicle is started. As it approaches the engine, the natural gas passes through a regulator to reduce the pressure. Then, it's fed into the fuel injector and into the cylinders. Sensors and computers in the vehicle help the gas burn cleanly and efficiently by adjusting the fuel-air ratio. LNG works similarly, but the liquid must first be heated before the process begins.
Jennifer Olvera, a graduate of DePaul University in Chicago, has been writing professionally for over a decade. In addition to covering the "green scene" for publications such as Where Magazine and Crain's, she has become one of the preeminent dining, food, and entertainment writers in Chicago. She has regularly been published in Chicago Magazine, Chicago Sun-Times, Chicago Tribune, Zagat, Citysearch.com, and Gayot.com.
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